Fluoropolymers are often used for their desirable properties, such as low surface tension, high thermal stability, and high transparency in the ultra-violet to the IR region of the electromagnetic spectrum. Low refractive index polymers have properties such as low coefficient of friction, improved wear/abrasion resistance, enhanced chemical resistance, low surface energy, water/oil and stain repellency and improved surface smoothness and gloss.
Commercially available low-refractive index polymer coating formulations have cured indices on the order of 1.36 to 1.42. For example, see U.S. Pat. No. 5,951,920 and U.S. Pat. No. 5,690,863 which cover “OPTI→CLAD” formulations. The patent literature shows coatings with cured refractive indices in the range of 1.37 to 1.43 (see U.S. Pat. No. 4,508,916, U.S. Pat. No. 4,511,209, U.S. Pat. No. 4,971,424, U.S. Pat. No. 5,024,507, and U.S. Pat. No. 5,239,026). There are recent reports of low refractive index materials ranging from 1.32 to 1.35 in a cured state (see U.S. Pat. No. 7,625,984, United States Patent Publication 2005/0261389, U.S. Pat. No. 6,703,463, and U.S. Pat. No. 6,249,638). However, these patents still show a need for a UV curable low refractive index that can possess a high loading of photo-initiators, which have a broad absorption range and exhibit adequate rigidity and adhesive strength.
Currently there exists the need for ultra low refractive index materials which can be cured with a wide range of curing wavelengths, contain greater amounts of photo-initiators, can provide excellent adhesion to glass, plastic and metal substrates, and provide adequate rigidity. Such coatings can be used not only in optical applications but can be extended to applications such as anti-dust, anti-fogging, anti-graffiti and bio-medical applications.